Hydraulic control valve with void control means



July 13, 1965 F. H. TENNIS 3,194,265

HYDRAULIC CONTROL VALVE WITH VOID CONTROL MEANS Filed May 2, 1962 2 Sheets-Sheet 1 big- , Francgs H. Tam-us July 13, 1965 H. TENNIS 3,194,265

AU CONTROL VALVE WITH Filed May 2, 1962 2 Sheets-Sheet 2 I0 I u mw-ww [8 92,3 I Fmmm l7h J f w F QQ/I' ma United States Patent 3,194,265 HYDRAULIQ QQNTRUL VALVE Wl'lH V011) 0NTRGL MEANE? Francis H. Tennis, Milwaukee, Wis, assignor to Hydraulic Unit Specialties Company, Town of Pewaulree, ounty of Waulresha, Wis, a corporation of Wisconsin Filed May 2, 1962, Ser. No. 191,868 7 Claims. ((31. l37-5%) This invention relates to hydraulic control valves of the type wherein a valve element is shiftable in a bore in a valve body to either of two defined operating positions, to selectively govern the direction of operation of a doule acting hydraulic cylinder or similar reversible hydraulic motor; and the invention refers more particularly to anti-cavitation or void control means in a hydraulic control valve of that nature.

A hydraulic control valve of the type here under con sideration comprises a body having therein a pressure fluid inlet connectable with a pump or other source of hydraulic fluid under pressure, a return fluid outlet connectable with a reservoir of the like, and one or more spool bores, each having a pair of service passages leading therefrom to motor ports in the body that are connectable with the ports of a reversible hydraulic motor. In each spool bore'there is a spool that is manually slidable in opposite directions from a neutral position to one or the other of a pair of operating positions. When the spool is in its neutral position it permits pressure fluid to flow from the inlet to the outlet for return to the reservoir; and in each of its operating positions the spool directs pressure fluid from the inlet to one of the service passages while communicating the other service passage with the outlet so that return fluid from a motor governed by the spool is sent back to the reservoir.

It often happens that a double acting hydraulic cylinder is employed to drive a mechanism that is subjected to substantial gravity or inertia loads which efiect more rapid movement of the mechanism in one or both directions than it can be propelled by its hydraulic cylinder.

Under these conditions, where the cylinder is driven by the load rather than driving it, the rate at which bydraulic fluid is supplied to the cylinder by the hydraulic pump may be insufficient to fill the void in the cylinder left by its rapidly moving piston, with undesirable con sequences that are well known to those skilled in the art.

To prevent drawing of a void under these circumstances it has been customary to provide such hydraulic systems with so called anti-cavitation or void control check valves which are normally closed but which open when the hydraulic motor is driven by its load and the piston is tending to draw a void, and which then permit return fluid from one end of the cylinder to be transferred back to its other end along with the fluid supplied thereto by the pump.

Such void control or anti-cavitation valves have ordinarily been incorporated in the body of the control valve by which the hydraulic mechanism is governed, and heretofore it has been the usual practice to provide one such void control valve for each of the service passages in the control valve body at which a void might be drawn under operating conditions. Thus in cases where a mum ber of control valve sections were ganged or stacked in a single assembly, for controlling several double acting cylinders from one location, there could be as many void control check valves in the assembly as service passages, with each pair of void control valves located in the valve body section that contained the spool with which the check valves were associated.

By contrast, it is a general object of the present invention to simplify the construction of spool type control valves having void control means embodied therein, and

lidddi ad to reduce the cost of such valves, by providing a single void control check valve which serves all of the service passages in a control valve assembly, Whether there be only two such service passages, associated with a single valve spool, or a substantially large number of them, associated with a plurailty of valve spools as in a stacked or sectional valve.

It is another object of the present invention to simplify. the construction of hydraulic control valves, whether having bodies cast in one piece or of the so called stacked or sectional type, and to minimize the cost of such valves by incorporating the void control means for the valve assembly in a manifold section having a chamber that is common to the service passages governed by all of the control spools of the valve.

It follows that it is another object of the present invention to make it possible to incorporate into the inlet section of a sectional control valve a combined pressure relief and vacuum relief valve of the type shown, for example, in the copending application of Francis H. Tennis and Donald G. Bethke, Serial No. 186,906, filed April 12, 1962, for Combined High Pressure Relief and Voi Control Valve, now Patent No. 3,112,763, so that the one composite valve performs all of the pressure relief and anti-cavitation functions for the entire valve assembly, serving all of the motor ports in the valve body, however, many there may be.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the herein disclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate several complete examples of the physical embodiments of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:

FIGURE 1 is a vertical sectional view of a sliding spool type of hydraulic control valve of sectional construction, comprised of two control sections, and incorporating the void control means of this invention;

FIGURE 2 is a fragmentary sectional view on an enlarged scale of a portion of the valve shown in FIG- URE 1;

FIGURE 3 is a horizontal sectional view taken on the plane of the line 33 in FIGURE 1; and

FIGURE 4 is a fragmentary vertical sectional View of a modified embodiment of the invention incorporating the combined high pressure and low pressure relief valve of the aforesaid application.

Referring now more particularly to the accompanying drawings, the numeral 5 designates generally the body of a hydraulic control valve which, though not essential to the invention, is illustrated as being of sectional construction. It comprises in general an inlet manifold section s, an exhaust manifold section 7, and a plurality of individual control or spool sections 8 and 9 which are assembled in stacked relationship with one another and with the inlet and exhaust sections, the latter being at opposite ends of the stack. Obviously the two spool sections shown are illustrative, since there might be only one such section in the stack, or any number of them. The two spool sections 8 and 9 may be substantially identical with one another, and each has a bore 11 therethrough in which a spool or valve element 12 is slidable in opposite directions from a neutral position, shown in FIGURE 3, to either of two operating positions at which the spool effects operation in one direction or the other of a double acting hydraulic cylinder or a similar reversi- 3 Y 7 ble hydraulic motor (not shown) connected with motor: ports 13 and 14in the spool section body.

Hydraulic pressure fluid from a source thereof such as r a pump (notshown) enters an inlet chamber 18in the inlet section 6 through aniinlet port 16. When the several spools are all in their neutral positions, pressure 2 fluid can flow from the inlet chamber 18 to a return fluid well '42- formed in a plug extension of the returnpassage'iand opens, into the. inlet chamber 20 in the exhaust manifold section 17 'by way of an open center passage 21 that extendsthrough. the several body sections, intersecting the bores 11 therein.

' The return fluid chamberopens to an outlet port ,22,"

ing position, it blocks the open center passage 21 and Y directs pressure fluid from the inlet chamber 18. into one or the other of a pair of service passages '27 and 28 that communicate'the spool bore with the motor ports ,13 and 14, respectively. In this case such diversion of fluid from the inlet chamber to a motor 'port is shown ,as being provided for byv a feederpassage 23 that opens from the inlet chamber 18 andextends through theseveral spool sections of: the body; and branched feeder passages 24 and 25 in each spool section which communia cate' the feeder passage with the spool bore. Those skilled in the art will recognize that the provision-of the feeder or supply passage 23 just describedtenables parallel operation of motors governed byrthe spools 12;v and'it will be appreciated that this arrangement is merely illus= trative, ,asthebranched feeder passages can be connected with the open center passage 21 to be supplied with pressure ifiui-d therefrom, in a series-parallel typea valve;

' Atthe same, time that the spool directs pressure fluid to oneof, its associated service passages it communicates the other service, passage with a branched exhaust pas: sage, -which communicates, with a return fluid passage or exhaust header 29 that extends through the several1 valve body sections and opens at one .endto the return- 'fluid chamber-ZO, whence such return fluid can of course pass to the outlet 22 and a reservoirconnected therewithn At its other end thereturn :passage 29 has aportion 31' that extends into the inletsection '6 of the valve :body,

chamber 18 throughan annula'r'yalve seat 44tw-hich faces, away from-the.returnpassagm and with which the head of the poppet isInormallyjengaged. If the valve body iisi'mounted'inthe p'ositionshown in FIGUREII, with the inlet section 16 uppermost and the exhaust header '291 'extending-1 substantially vertically downwardly therefrom, gravity can :be 'reliedfiuponto bias the vcheck valve poppet'onto itsseath Preferably, i Qwever, the. stem .rportion oftheivalve element has'awell therein in which a light jooiled compression, spring45 is 'confined,pthat reacts ,between' therbott'orn 0f the well .42; in the plug. 43 and thev'alve' element to insure thatthe poppet V V willbe biasedstowardits seat in anyattit ideiof: the valve body; H i

To insure V the void control mechanism preferably includes :alrelief or-back pressurevalve 47 which at'all timestendsto maintainreturn fluid in the ,eXhaustLheaderE -ZQ at. a uniform' VacuumrRe'lief Valve, now Patent No. 3,100,503. Die-, tails of that valve unit'canibe found; in'sa-id'copending application, but briefly, it comprises I(see;-FIG U RE "2) a body 91iin1whi'ch a plunger-likezouter poppet192 "is axially? slidablefltoward ,andiifrom engagement 'with a seat 93 that faces towardthe return fluid chamber 2tl= and V coaxially surroundsithe outlet of {the exhaust header 29,1

The outer poppet; which is :a: low pressure responsive and whichis branched, asfat 33 and 34, for communica- 7 tion with the inlet chamber 18. However, communication between theinlet chamber and the return passage is, normally blocked by apressure relief valve 36 which con-t trols'the branch 33 and by a void control check valve 37 which controls the branch 34.

The pressure relief valve 36 can be of a conventional type and needs nodescriptionhere. Sufiice .itto sayjthat it is responsive to pressure of fluid in the inlet chamber 18, and ,whensuch pressure exceeds a predetermined value the relief valve unseats and permits pressure fluid to flow from the inlet chamber, intov the return passage 29 by way Of the branch 33; The short passage comprising the;

exhaust header branch 33 is of course formed witha suitablerannular seat against which the relief valve ele ment is normally engaged .under bias. 7 The void control valve 37 can likewise be of-a know type, comprising a check'valve that'opens when pressure the :inlet: chamber. 18, as may happen when one of: the v. spools 12 is in an operative position and a hydraulic motor,

governed thereby is being driven by its load in such a I of fluid in the return passage .29 exceeds that offluidini valve element, has an axially extending but eccentricjpas sage 94 therein that communicates theexhaust header 29 with 'the cylinder space in the ivalve body '91 is, behind saidpoppet. 1 A coiled compressionxspring 95 'cov operates with fluid in the body; 91 behind the' outerpoppet;

to urge the latter: towards its 'seat:93. Pressure of fluid in the returnfluid chamber 20 isexerted upon arr-annular. forwardly facing surface: 96-on the outerrpoppethspaced behind its seat engaging surface,;and when such pressure exceeds that in the exhaust headeryZQjthe outer poppet moves. away 'fromits seat .93 This, conditioncould' occur 7 in a situation where there :was an extremeltende ncy to draw a voidin'one of the service passages, so that return 'fluid from the other service :passag'e plus pressure fluid supplied by .the pump wouldbe insufficient to supply voidcontrolrequirements, and in that eventfluid from the 5 return fluid chamber ZOjtand a reservoirjconnectedthere! with could, flow back into the :cxhaust, header- 29, and

thenceto the service passage at which the void was being drawn,-to supply the, deficiency.

Slidable in the ,outerpoppet is an 'inner pilot poppet 97 which normally blocks flow of 'fluidth'rough a vent passage in the, outer; poppet and-which iswbiased forwardly,

relative to the; outeripoppet by a compression ;sprin'g 98.

The vent passage is defined'bythe axial passage 94 in the outerpoppet, a coaxial borei99 in'thejouterpoppet reacts against-=a spring seat 102 that isthr'eaded into the 7 rear of the outer poppet and isradjustableaxiallybymeans of an ,adjustingmechanisin ,103 described in ltheafo'resaid copending application Serialv No. 153,415

that is threaded into the wall 5 of the inlet ,section; The branch 34-ofthe return passage E with which the void control-valve cooperates is Ian's: axial dependable operation-of thei'check valve 37 The inner poppet is moved off to its seat in response to fluid pressure above a predetermined value in the exhaust header 29, which pressure is manifested upon a small plunger 104 that is freely movable axially in the bore 99. So long as such fluid pressure exceeds the value for which the pilot spring 98 is adjusted, the plunger will hold the pilot poppet 97 unseated, permitting fluid to be vented from behind the outer poppet through the vent passage 94, 99, 100 and 101; and such venting of fluid from behind the outer poppet permits the latter to be moved off of its seat in response to the pressure of fluid in the exhaust header 29 manifested upon its front end. When the valve unit is thus effecting high pressure relief, with the small plunger 104 in its rearward position, said plunger partially blocks the intersection of the bore 99 and the eccentric passage 94, restricting flow of fluid into the rear portion of the body 91 and thus preventing chattering of the outer poppet. It will be understood that the force of the pilot spring 98 is set to maintain a constant pressure differential between the fluid in the exhaust header 29 and fluid in the return fluid chamber iii, of a value small enough not to interfere with operation of motors connected with the control valve, but suflicient to insure rapid and dependable opening of the void control check valve 37.

Instead of the dual function valve 47, the outlet of the exhaust header could be a restricted orifice, in which case back pressure would be manifested upon return fluid in the exhaust header 29 only at high flow rates, such as occur when a void tends to be drawn in one of the service passages. In either event the flow restricting means causes the check valve 37 to be unseated before an actual void can bedrawn in the service passage to which pressure fluid is being directed by the valve spool.

In the embodiment of the invention illustrated in FIG- URE 4 the void control means is incorporated in a composite valve assembly 51 that also provides the high pres sure relief valve, and which is of the type disclosed in the aforesaid application of Francis H. Tennis and Donald G. Bethke, Serial No. 186,906, now Patent No. 3,112,763. In this instance the exhaust header 29 is communicable with the inlet chamber 18 through a single branch passage 133 that is controlled by the composite valve assembly 51 and which is of course normally closed by said valve assembly. In other respects the valve illustrated in FIG- URE 4 can'be identical with that shown in FIGURE 1.

The valve assembly 51 comprises a body 52 which is open at its front and provides a cylinder at its rear in which a tubular low pressure poppet 53 is slidable toward and from engagement with a seat 54 formed coaxially with the branch passage 133. The low pressure poppet is biased toward the seat by means of a coiled compression spring 55 that reacts between said poppet and the valve body 52. At its front the low pressure poppet is formed with a forwardly facing shoulder 59 against which the pressure of fluid in the exhaust header is manifested, and whenpressure of fluid in the inlet chamber 18 falls below that of fluid in the exhaust header 2.9, the rear portion of the cylinder is evacuated through the bore in the low pressure poppet, allowing the latter to move rearwardly off of its seat in response to the force exerted upon shoulder 59 by fluid in the exhaust header.

The high pressure relief valve comprises a tubular high pressure poppet 61 coaxially slidable in the low pressure poppet and having a stem portion 62 slidably guided in the rear portion of the low pressure poppet and an enlarged head portion 63 engageable with a coaxial rearwardly facing annular seat 64 at the front of the low pressure poppet. The high pressure relief passage comprises the front portion 65 of the bore in the low pressure poppet and radial ports 66 in the side of the low pressure poppet, behind the seat 64 therein, that open from its bore to the exhaust header 29. The high pressure poppet is normally biased into engagement with its seat 64 by means of a coiled compression spring 67 encircling its stem portion and reacting between its head and the low pressure poppet, but when pressure in the inlet chamber 18 exceeds a high value determined by the biasing force exerted by said spring the high pressure poppet is moved off of its seat, permitting pressure fluid to flow through the ports 66 and to the exhaust header.

For a more detailed description of the valve assembly 51 reference can be made to the aforesaid copending application.

It will be evident that a valve like the above described dual function valve 4 7 could be used in place of the last described composite valve assembly 51, and in that event the pilot spring $8 would of course be adjusted to a higher relief value, suflicient to maintain normal system pressure in the inlet chamber 18. The provision of a composite or dual function valve to control communication between the inlet chamber and the exhaust header has the obvious advantage of compactness, but has the further important advantage that its low pressure poppet moves off of its seat in a direction counter to that in which it permits fluid to flow. Such action of the low pressure poppet permits substantially unrestricted flow of fluid, as contrasted with the poppet of a more conventional check valve, which moves in the direction in which it permits flow to take place and which presents a substantial restriction to the flow that it permits because fluid is always compelled to flow around it and also around any spring that may be biasing it toward its seated position. The importance of this feature will be apparent when it is considered that when a void is developing in a service passage the pressure differential between the inlet chamber and the exhaust header is relatively low, even with the flow restricter 47, and hence any substantial restriction presented by the check valve means would interfere with the desired free flow.

It will be evident that the void control means of this invention is applicable to hydraulic control valves which are not of the sectional type herein illustrated and described, although it is particularly advantageous in valves of that type because it enables but one check valve in the inlet section to serve any number of motor ports in the valve body, eliminating the need for pairs of check valves in the individual spool sections.

From the foregoing description taken together with the accompanying drawings it will be apparent to those skilled in the art that this invention provides void control or anti-cavitation means in a hydraulic control valve of the sliding spool type whereby a single check valve accommodates each and every one of the service passages in the valve body, permitting a valve incorporating the inven tion to be manufactured at lower cost and with greater facility than previous valves of comparable type.

What is claimed as my invention is:

1. A sectional control valve of the type comprising an inlet section having an inlet chamber into which pressure fluid from a source thereof can be introduced, a return fluid manifold communicated with an outlet, and at least one control section confined between the inlet section and the return fluid manifold, of the type in which a spool is slidable to each of a pair of operating positions to communicate either of a pair of service passages in the control section with a supply passage therein that connects with the inlet chamber, while communicating the other service passage with a return passage in the control section, said valve being characterized by the following:

(A) that all of the return passages are connected to a common exhaut header having one end communicating with the return fluid manifold and which extends through each control section crosswise of the spool therein;

(13) that the other end of the exhaust header is communicable with the inlet chamber through a pressure relief valve which normally blocks communication between the inlet chamber and said exhaust header, but is responsive to pressure of fluid in the inlet '7' chamber in excess of a predetermined valueto-open and permit flow of fluid therefrom to the exhaust headeryand I i (C) ,thatsaid other end of the exhaust header is also communicable with the'inlet chamber through a void 7 control check valve which. cooperates with the pressure relief valve-to normally-block communication 1 between the inlet chamber and the exhaust header,

but is responsive to pressure of fluid in the exhaust header which exceeds that of fluid in the inlet chamher to open and permit'such communication so that whenever'a control spool is in one of its operating 1 positions andythe pressure of return fluid from the service passage then communicated with the exhaust her, fluid can flow from saidlast named serviceheader exceeds the pressure of fluid in the inletchampassage to the inlet chamber'via the exhaust header for flow to the other service passage along with pressure fluid entering the inlet chamber from a source;

2. A control valve of the type having a body in which there are a plurality of spool bores, eachcommunicated with a pair of service passages, and a spool slidable in each bore to either of a pair of operating positions at reach of which the spool directs pressure fluid from an inlet chamber in the valve body to one of the service passages associated with its bore and directs return fluid from its other associated service passage to return passage means in the bodyleading to an outlet therein, said control valve being characterized by: said return passage, means comprises an exhaust header common to the servic'e; i, passages of all the bores, and extending crosswise of the;

bores; a unitary valve mechanism governing a void controlfpassage in the valve bodythat connects one end of [the exhaust header with the inlet chamber, said valve mechanism providing a check valve controlling direct communicationbetween theinlet chamber and the exhaust header and preventing such communication as long 1 as pressure of fluid in the inlet chamber exceeds that of fluid in the exhaust. header but responsive to pressure of fluid in;the exhaust header which exceeds thatin the inlet. chamber to open and permit return fluid from any service passage then communicated with the header to flow to the inlet chamber and thence to any service pas:

sage to which pressure fluid is then being directed, so'that v a single void control check valve serves all service pas,-

sages in the valve body, and said mechanism also providing a normally closed high pressure relief valve which opensto establish communication between the inlet cham- 5 her and the exhaust header through said void control,

' passage, in response to an abnormally high pressure condition in the inlet, chamber.

3. A control valve of the type having a body in which a there are a plurality of spool bores, each communicated with a pair of service passages, and a spool slidable in each bore to either of a pair of operating positions at each of'which the spool directs pressure fluid from an inlet chamber in the valve body to one of the service passages" associated Withiits bore and directs returnfluid from :itS other associated service passage to returnpassagemcans in the body leading to an outlet therein,-'said control valve being, characterized by; a single check valve in a;void

control passage in the valve body, contro lling direct com-1 1 munication between the inlet; chamber and the return passage' means and preventing such communication as long as pressure of fluid in the inlet chamber exceeds that of fluid in the return passage means but responsive to pressure of fluid in theireturn passage means which exceeds that in theinlet chamber to openand permit return fluid from iany service passage, then communicated with .7

the return passagerneans to flow to the inlet chamber and thence to any service passage to which pressure fluid .is; then being directed, so that the single void control check valve serves all service passages in the valve body; said return passage means comprising an exhaust header in v V the body having one end opening into the inlet-chamber;

i and its other endcommunicating with the: outlet," the 1 check'valve being located attheyfirst' desigiitated endf oi 'the header; and further; characterized byimeans at said ,othe riend portion of the header torestrict communication with'the outlet so that pressurelinethe header ;will rise' 1 quickly as soon as return fluid from any oneot the service;

passages flows-thereinto at an abnormally high rate, thus insuring prompt unseating ofthe check valve.

4. A control valve of the type-"having a.

to either of a pair of, operating positionsat each; of which the spool directs 'pressurefluidfrom an inlet ichamberiin the valve body to one of a pair ofservice passages: in the 4 3 valve body, and directs return fiuidi'fr-on theother; service .passage'to a return passage iu the, body leading to -an outlet therein, said control valve being'characterized by:

(A) the; return'passages lead tothe "outlet .throughja common 'exhaustheadergthat has oneIend connected with the" inlet chamber, gand whichlheader extends" through the body at a location to I Wise ofthe SPO-O'LbOI'CQi (B) valve meansin the oneisid'e and crossher, said valve means including 7 V the: inlet charnber. directly to lthe' exhaustheader,

(2) and normally closed low-pressure relief valve 7 a mechanism that opens Wheneverthe pressureof fluid in the-inlet chamber drops to arvalue below ,that'of fluid in the exhaust'headerg' i (C) and means affording restricted-"communication her;

tween the exhaust header and thebody outlet.

(A) means comprising};combination,exhaust header:

' and void cointr-olpassagea for communicating both;

the service'p'assages:and the;fluid-supply means'with i the exhaust outlet;

(B)'*'a normally closed pressuiegresponsive ivoid con trol valve in the body controlling communication he;

tween theexhaust header andtl eafluid supply means,

said void controlvalve beingfadapted to, open in either operating positionfof'theyalveelernentpto enable exhaust fluidfrom the service, passage then .com-

municated with thege'xhausrheader toflow: tolthe fluid supply "-means whenever the pressure ofsuch 6. Th'e control valveiof claim ii, fwhereinrs'aid last a designated means comprises 7 a pressu e sensitive valve def vice. which is biased toward an iextremetrestricting positron but opens to a less restricting position in response torislngpressure'in the exhaustaheadera i V 7. The control valve of cl-aim-. 4,r wherein said "last named means comprises" V (1) high pressureaelie f valve termined desired value to allow :fluiditoflow from the'header-to the outlet, v r

V V 7 7 body wherein there is a spool boreand a spool slidable in the spool bore,

utmenusc mm i t;' tion between the; exhaust header and the inlet; cham- I (1 ;high pressure relief valve' mechanismy'which a is normally closed but op'ens whenever thepies- 3 surepf; fluid in the inlet ch'amber rises to an ah: normally highjvalue to allow fluid ;-to flow from" 5. 'A control;-valve or the type having a body :with a valve element movable therein to each of a pair of operatj-i; ing positions to communicateeither offa'pair ofservice 7 passages with fluidsupply means in tlie body and to communicate the othcrservice passage with ganexhaust outletj in the body, char'acterized by T exhaustfluid exceeds that offluid in the fluidsupplyi (C) said exhaust header-commun catingwith the fluidm mechanism'whichiis normally closed but which opens whenever the pres,- sure of fluid in the exhaust header rises to a prede' (2) and low'. pressureirelicf; valve mechanism which is I References Qited by the Examiner UNITED STATES PATENTS 2,856,960 10/58 Stacey 137-62I 2,873,762 2/59 Tennis 137--621 2/60 Dolan 137621 XR 8/60 Vander Kaay 137-621 XR 9/60 Krehbiel 137-596.13 9/60 Krehbiel 137--622 FOREIGN PATENTS 3/55 Great Britain.

M. CARY NELSON, Primary Examiner. 

1. A SECTIONAL CONTROL VALVE OF THE TYPE COMPRISING AN INLET SECTION HAVING AN INLET CHAMBER INTO WHICH PRESSURE FLUID FROM A SOURCE THEREOF CAN BE INTRODUCED, A RETURN FLUID MANIFOLD COMMUNICATED WITH AN OUTLET, AND AT LEAST ONE CONTROL SECTION CONFINED BETWEEN THE INLET SECTION AND THE RETURN FLUID MANIFOLD, OF THE TYPE IN WHICH A SPOOL IS SLIDABLE TO EACH OF A PAIR OF OPERATING POSITIONS TO COMMUNICATE EITHER OF A PAIR OF OPERATING POSITIONS TO COMTROL SECTION WITH A SUPPLY PASSAGE THEREIN THAT CONNECTS WITH THE INLET CHAMBER, WHILE COMMUNICATING THE OTHER SERVICE PASSAGE WITH A RETURN PASSAGE IN THE CONTROL SECTION, SAID VALVE BEING CHARACTERIZED BY THE FOLLOWING: (A) THAT ALL OF THE RETURN PASSAGES ARE CONNECTED TO A COMMON EXHAUST HEADER HAVING ONE END COMMUNICATING WITH THE RETURN FLUID MANIFOLD AND WHICH EXTENDS THROUGH EACH CONTROL SECTION CROSSWISE OF THE SPOOL THEREIN; (B) THAT THE OTHER END OF THE EXHAUST HEADER IS COMMUNICABLE WITH THE INLET CHAMBER THROUGH A PRESSURE RELIEF VALVE WHICH NORMALLY BLOCKS COMMUNICATION BETWEEN TH EINLET CHAMBER AND SAID EXHAUST HEADER, BUT IS RESPONSIVE TO PRESSURE OF FLUID IN THE INLET CHAMBER IN EXCESS OF A PREDETERMINED VALUE OF OPEN AND PERMIT FLOW OF FLUID THEREFROM TO THE EXHAUST HEADER; AND 